Essential to normal heart function are four heart valves, which allow blood to pass through the four chambers of the heart in one direction. The valves have either two or three cusps, flaps, or leaflets, which comprise fibrous tissue that attaches to the walls of the heart. The cusps open when the blood flow is flowing correctly and then close to form a tight seal to prevent backflow.
The four chambers are known as the right and left atria (upper chambers) and right and left ventricles (lower chambers). The four valves that control blood flow are known as the tricuspid, mitral, pulmonary, and aortic valves. In a normally functioning heart, the tricuspid valve allows one-way flow of deoxygenated blood from the right upper chamber (right atrium) to the right lower chamber (right ventricle). When the right ventricle contracts, the pulmonary valve allows one-way blood flow from the right ventricle to the pulmonary artery, which carries the deoxygenated blood to the lungs. The mitral valve, also a one-way valve, allows oxygenated blood, which has returned to the left upper chamber (left atrium), to flow to the left lower chamber (left ventricle). When the left ventricle contracts, the oxygenated blood is pumped through the aortic valve to the aorta.
Certain heart abnormalities result from heart valve defects, such as valvular insufficiency. For example, mitral valve insufficiency, also known as mitral regurgitation, is a common cardiac abnormality where the mitral valve leaflets do not completely close when the left ventricle contracts. This allows blood to flow back into the left atrium, which then requires the heart to work harder as it must pump both the regular volume of blood and the blood that has regurgitated back into the left atrium. Obviously, if this insufficiency is not corrected, the added workload can eventually result in heart failure.
One option to correct valve defects is complete valve replacement. This intervention, however, is quite invasive and traumatic. There are more conservative surgical interventions that are less traumatic than implanting valvular prostheses. These approaches include valve leaflet repair, chordae tendinae shortening or replacement, and or valve annulus repair also known as annuloplasty. One example where annuloplasty procedures have been developed is in the field of mitral valve insufficiency correction.
Mitral valve insufficiency typically results from a change in the size and shape of the mitral valve annulus. Mitral valve annuloplasty involves reestablishing the normal shape and size of the mitral valve annulus so that it can effect full closure of the valve leaflets.
There have been a number of annuloplasty approaches to repair the mitral annulus of a patient's heart. Dr. Norberto G. De Vega developed a procedure in the early 1970s. One laces a suture along the periphery of a compromised portion of the heart valve. The suture is drawn in a “purse string” manner to cinch the tissue and reduce the size of the valve opening. Then the suture ends are knotted. Although the procedure can reduce the size of the valve opening and improve valve efficiency, it is not free from drawbacks. One disadvantage of this approach is that the sutures can pull out of the tissue and “guitar sting” across the valve annulus. The purse string also may cause tissue bunching, which may distort the natural shape of the valve.
Other approaches to improve valve function (e.g., with the mitral or tricuspid valves) include tissue plication devices and reinforcement of the valve annulus with annuloplasty rings. These approaches also are claimed to reestablish the original annulus size and shape and/or prevent further annulus dilation.
Both rigid and flexible annuloplasty rings have been developed. Rigid rings, which generally tend to dictate the shape and contour of the mitral valve annulus, have been considered to somewhat compromise the natural flexibility of the annulus. Flexible annuloplasty rings emerged to provide some degree of compliance in the valve annulus so that the valve could maintain normal physiological motion throughout the cardiac cycle of a beating heart. This is in addition to providing annulus reinforcement. However, it is believed that among the drawbacks of these rings is that they may fold or crimp during implantation and thereby undesirably reduce the size of the valve (e.g., mitral) opening. Also, the sutures used to secure the ring may cause scarring and stiffening of the valve annulus and reduce annulus flexibility over time.
C-shaped bands or partial annuloplasty rings also have been developed. These devices can be attached solely to the posterior portion of the valve annulus which eliminates the need to attach material to the anterior portion of the annulus. The annulus is fibrous and generally does not require plication and/or reinforcement. Thus, the partial rings can preserve the normal function of the anterior portion of the annulus. Full and partial ring devices are disclosed, for example, in U.S. Pat. No. 3,656,185, which issued to Carpentier.
Other attempts to improve upon valve repair procedures, including the De Vega approach and the use of rigid, flexible, and partial rings, include that described in U.S. Pat. No. 5,450,860, which issued to O'Connor, U.S. Pat. No. 6,183,512B1, which issued to Howanec, Jr. et al., and U.S. Pat. No. 6,250,308B1, which issued to Cox.
The O'Connor patent discloses a plication approach, particularly suitable for use with an annuloplasty operation on heart valves (e.g., mitral or tricuspid valves). The approach involves a ligament, which can comprise a wide, flexible strip of expanded polytetrafluorethylene or similar material, and sutures to retain the ligament in place. The ligament has at least an end of constricted diameter and a needle attached thereto, or it can have two constricted ends and a needle attached to each of the ends. This construction permits the ligament to be drawn through an area of tissue to be plicated. Once in place, a first end of the ligament is anchored, preferably with sewing of conventional sutures through the ligament, and the tissue is cinched along the length of the ligament to provide the desired amount of plication. Once the tissue is correctly oriented, the second end of the ligament is then likewise anchored in place, again preferably through the use of a suture sewn through the ligament.
The Howanec patent describes a system that includes an elongate flexible band with a needle attached to one end of the band and a fit adjuster attached to the other end of the band. The needle is used to introduce the band into the atrioventricular groove (hereafter “AV groove”) and then pull a portion of the band out of the tissue. After the band is so implanted into the AV groove, a fit adjuster is used to couple the exposed ends of the band and size and position the band in the annulus. After the band is pulled to cinch the tissue in the AV groove until the valve annulus is reconfigured to an optimal shape, the band can be secured to the valve annulus with sutures and the exposed portions of the annuloplasty system removed.
The Cox patent describes a system that comprises a combined annuloplasty ring implant, which has a rigid section and a flexible section. A needle is coupled to one end of the implant. The needle facilitates introducing the implant into the fatty pad of the AV groove, which surrounds the valve annulus, at one end of the posterior portion of the annulus and pulling one end portion of the implant out of the AV groove in the vicinity of the other end of the posterior portion of the annulus. The flexible section of the ring extends adjacent to the flexible posterior portion of the annulus, while the rigid section of the ring spans the substantially rigid inter-trigone section of the annulus. Cox advances that with this procedure one need not suture the flexible section directly to the mitral valve annulus, thereby substantially eliminating scarring and stiffening of the annulus. In one example, the flexible material is also elastic to accommodate the expansion and contraction of the annulus, in addition to flexing. The system further includes means for joining the ends of the ring, which are positioned along the inter-trigone section, after the needle is removed. Sutures can be added to secure the annuloplasty ring to the annulus, for example, along the inter-trigone section.
Other plication and valve repair approaches are disclosed in PCT International Patent Application Nos. PCT/US01/42653 and PCT/US01/31709, which are co-owned by the assignee of the present disclosure and entitled “Minimally Invasive Annuloplasty Procedure and Apparatus” and “Minimally Invasive Valve Repair Procedure and Apparatus,” and which published under International Publication Nos. WO 02/30298 and WO 0230295, respectively. These approaches, in-part, address various inherent disadvantages with prior open heart surgical procedures as described, for example, by F. Maisano, et al. in their article entitled “The double-orifice technique as a standardized approach to treat mitral regurgitation due to severe myxomatous disease” which appeared in European Journal of Cardio-thoracic Surgery, Vol. 17 (2000) 201-205. Disadvantages associated with such open-heart procedures include cumbersome suture management, timely knot tying steps, pain, and long recovery time.
Generally, known annuloplasty ring and band recipients are required to undergo anticoagulation therapy for a minimum of several months post-operatively due to the high risk of prosthesis-induced thrombosis. However, anticoagulation therapy increases the risk of bleeding complications due to the inhibition of blood clot formation.
Applicants believe that there remains a need for improved valvular repair apparatus and methods.